1. Field of the Invention
The present invention relates generally to an image forming apparatus including a sound absorbing device utilizing a Helmholtz resonator.
2. Description of the Related Art
An electrophotographic image forming apparatus typically emits, when forming an image, sounds including operating sounds of various drive units and rotational sound of a polygon mirror. Example configurations for absorbing sounds emitted during image formation are disclosed in Japanese Laid-open Patent Application No. 2000-235396 and Japanese Laid-open Patent Application No. 2001-11745, each disclosing an image forming apparatus including a sound absorbing device utilizing a Helmholtz resonator.
A Helmholtz resonator is made of a cavity having a certain volume and a port portion connecting the cavity the outside air. Frequency f of sound to be absorbed by a sound absorbing device utilizing a Helmholtz resonator is given by Equation (1) below
                    f        =                              c                          2              ⁢                                                          ⁢              π                                ⁢                                    S                              V                ⁡                                  (                                      H                    +                                          Δ                      ⁢                                                                                          ⁢                      r                                                        )                                                                                        (        1        )            where V is the volume of the cavity, S is opening area of the port portion, H is the length of the port portion in the direction in which sounds come in, c is the speed of sound, and Δr is open end correction.
Some type of image forming apparatuses includes a hinged exterior cover operable to open and close relative to an apparatus body so as to expose a consumable, which can be a toner bottle and/or a process cartridge, when a user replaces the consumable. Such a hinged exterior cover is typically arranged in one side surface, which faces a user operating a control panel of the image forming apparatus, of side surfaces of the image forming apparatus. Accordingly, if sound leaks out of the apparatus from the side surface facing the user, the sound is likely to be perceived as objectionable noise.
One type of such a hinged exterior cover of an image forming apparatus is a double-door hinged cover hinged on the right and left, an example of which is disclosed in Japanese Laid-open Patent Application No. 2000-235396. However, recent image forming apparatuses generally employ a hinged exterior cover of a vertically-pivotable type configured to rotate about a pivot shaft arranged at a lower end portion of the hinged cover from a closed state to an open state in a manner to tilt toward near side (outer side). Such a vertically-pivotable hinged exterior cover is advantageous in that even if an operator who is opening the hinged exterior cover releases his/her hand therefrom, the hinged exterior cover can rotate under its own weight to the open state. However, the hinged exterior cover can be damaged by a shock imparted thereto when, after rotating under its own weight, the hinged exterior cover stops rotating suddenly at a position where the hinged exterior cover is in the open state. For this reason, a hinged exterior cover is required to have greater strength than such a double-door hinged cover as that disclosed in Japanese Laid-open Patent Application No. 2000-235396.
Thus, there is a need for an image forming apparatus capable of reducing leakage of sound from a side surface, in which a vertically-pivotable hinged exterior cover configured to pivot about a pivot shaft arranged at a lower end portion of the hinged exterior cover is provided, of the image forming apparatus while simultaneously increasing strength of the hinged exterior cover.